Down-regulation of MicroRNAs 222/221 in Acute Myelogenous Leukemia with Deranged Core-Binding Factor Subunits

Abstract

Core-binding factor leukemia (CBFL) is a subgroup of acute myeloid leukemia (AML) characterized by genetic mutations involving the subunits of the core-binding factor (CBF). The leukemogenesis model for CBFL posits that one, or more, gene mutations inducing increased cell proliferation and/or inhibition of apoptosis cooperate with CBF mutations for leukemia development. One of the most common mutations associated with CBF mutations involves the KIT receptor. A high expression of KIT is a hallmark of a high proportion of CBFL. Previous studies indicate that microRNA (MIR) 222/221 targets the 3' untranslated region of the KIT messenger RNA and our observation that AML1 can bind the MIR-222/221 promoter, we hypothesized that MIR-222/221 represents the link between CBF and KIT. Here, we show that MIR-222/221 expression is upregulated after myeloid differentiation of normal bone marrow AC133(+) stem progenitor cells. CBFL blasts with either t(8;21) or inv(16) CBF rearrangements with high expression levels of KIT (CD117) display a significantly lower level of MIR-222/221 expression than non-CBFL blasts. Consistently, we found that the t(8;21) AML1-MTG8 fusion protein binds the MIR-222/221 promoter and induces transcriptional repression of a MIR-222/221-LUC reporter. Because of the highly conserved sequence homology, we demonstrated concomitant MIR-222/221 down-regulation and KIT up-regulation in the 32D/WT1 mouse cell model carrying the AML1-MTG16 fusion protein. This study provides the first hint that CBFL-associated fusion proteins may lead to up-regulation of the KIT receptor by down-regulating MIR-222/221, thus explaining the concomitant occurrence of CBF genetic rearrangements and overexpression of wild type or mutant KIT in AML.

Putative genomic characteristics of BRAF V600K versus V600E cutaneous melanoma

“…Up-regulation of mir-222 results in dramatic loss of KIT transcript and c-Kit protein by targeting the 3′-untranslated region (UTR) of KIT in papillary thyroid carcinoma [26], gastrointestinal stromal tumors [27, 28], erythroleukemic cells [29], prostate cancer [30], acute myelogenous leukemia [31], cutaneous melanoma [32] and human umbilical vein endothelial cells (HUVECs) [33]. …”

“…PLZF ( ZBTB16 ) expression was not differential between V600K and V600E subtypes, however (data not shown). Other transcription factors known to regulate mir-222 expression include AML1 (RUXN1) [31], AP-1 [40], FOSL1 [42] and NF-κB and c-Jun [49]. Although FOSL2 and RUNX3 were significantly down-regulated in V600K tumors compared to V600E tumors, whether either of the two played a role in the differential regulation of mir-222 expression is unclear.…”

The miR-200 and miR-221/222 microRNA Families: Opposing Effects on Epithelial Identity

“…Other transcriptional repressors of miR-221/222 function in a cell-type specific manner. For example, in AML cells, the AML1 protein binds to the promoter of miR-221/222 and represses transcription (135). In melanoma cells, a transcriptional repressor, PLZF (promyelocytic leukemia zinc finger) binds to the promoter of miR-221/222 (136).…”

Prognostic markers in AML: focus on CBFL

“…Moreover, we have recently reported that CBF genetic abnormalities can target microRNA genes (Mir222/221) involved in the regulation of the KIT receptor, leading to KIT overexpression in CBFL. 8 Furthermore, it has been postulated that mutations of the KIT gene may drive the WBC proliferation in CBFL, and the clinical observations that affected patients with t(8;21) appear to have a higher WBC count and WBC index at presentation and a higher frequency of EML might support this hypothesis.…”